Potentiometer



Oct. 1l, 1960 J. CLAYTON, JR., ETA. 2,956,253

POTENTIOMETER Filed Feb. 11, 1959 FUE- E /5 /6 Z6 2 i l Z9 JZ 74 Z0 /44 j? K f y 70 J4] /1370 A 74 JZ United States Patent O` POTENTIOIVIETER John Clayton, Jr., Maynard, and Donald E. Trubey, Westford, Mass., assignors to Waters Manufacturing, Inc., Wayland, Mass., a corporation of Massachusetts Filed Feb. 11, 1959, Ser. No. 792,585

1'4 Claims. (Cl. 338-137) This invention relates to potentiometers, and more specifically to rotary potentiometers of the type in which the rotor bears more than one wiper contact, the wiper contacts being mutually insulated and electrically connected to separate terminals.

In most potentiometers, the movable wiper assembly bears a single movable contact touching the fixed portion of the resistance element of the potentiometer (it will be understood, of course, that the term potentiometer as herein used includes variable resistances). However, for certain purposes, there are employed potentiometers, particularly of the rotary type, having more than one movable contact or wiper, mutually insulated and brought out to separate terminals for their desired separate electrical connections in the circuit in which employed. Such structures may be employed for mere gauging (i.e., mechanicall interconnection), of electrically independent wipers, as in a structure wherein there are incorporated in a singlehousing two or more separate resistance elements, each with its own wiper; more commonly they are used for the production of voltages or resistance values from a single resistance element which are identical except for a fixed angular difference in the relation between rotational position of the potentiometer shaft and the respective voltage or'resistance amplitudes appearing at the wiper terminals. One fairly common use of such multi-wiper constructions is in the so called sine-cosine potentiometer, in which the resistance Varies sinusoidally around the entire resistance element, so that when the shaft is rotated at constant speed with appropriate direct voltage impressed across the element, each of the wipers produces a sinusoidal signal at its terminal, the wipers being arranged on the shaft at a 90 angle, thus generating a sine signal and a cosine signal in response to the rotation of the shaft.

Where such potentiometers are designed for precision work, serious problems of cost and complexity are introduced. It is necessary not only to provide suitable means for mounting the wiper contacts on the shaft at the desired relative longitudinal locations, but also to provide for adjustment of the exact phasing or angular relation between the contacts. In the most elementary form of such potentiometers, the wipers and their associated slip-ring contacts (employed to bring the wiper signals to external terminals) are merely individually mounted on the common shaft in separate assemblies like those used in potentiometers employing one wiper. In another type of mounting for such contacts, the phasing and other aspects of the relative positioning of the two contacts are accomplished in the design and fabrication of a single mounting assembly. However, the assemblies of this type lheretofore devised present solutions to the problem of cost which are far froml adequate as regards minimizing the cost differential which is added to the cost of making a single wiper potentiometer, both as regards cost of the contact assembly and as regards cost of installing the assembly in the potentiometer, the latter being a particular problem.

Patented Oct. 1l, 1960 lce Irrespective of the exactness of machining and other methods used in producing such mounting assemblies as heretofore devised, it is found that it is nevertheless necessary to provide an adjustment for the phase angle between the wiper contacts, since the contacts themselves are, in precision potentiometers, relatively delicate and easily deformed and are, particularly in miniature-type potentiometers, so small that accurate relative positioning of the exact points of contact of the respective wipers with the fixed resistance element requires that the phase angle be adjusted to its proper value after the wipers are actually installed in the potentiometer. Such requirements have heretofore made the task of assembly and adjustment a difiicult one, requiring multiple adjustments of a plurality of screws before the final adjustment is complete. A further difficulty with this type of structure as heretofore employed has been the fact that such structures have been suitable for use only with a particular phase angle, i.e., it was necessary to provide a completell new construction for any desired phase angle, since the multiple wiper assemblies Iheretofore devised did not provide for adjustment of the phase angle over a large range; one could not, with a single design of the contact assemblies heretofore otherwise suitable, produce potentiometers having wipers with a substantial range of phase angles. In order to use contact assemblies of types heretofore available as universal assemblies, to produce exact phase angles over a substantial range in potentiometers designed for a variety of particular uses, it was heretofore necessary to introduce a. great deal of complexity in construction and installation. Since cost is a very important factor in the use and distribution of potentiometers, reductions in these cost factors are of substantial commercial importance not only in satisfying known needs for such potentiometers, but also in stimulating -their use for new purposes.

It is accordingly the principal object of the present invention to provide a construction for a multiple wiper assembly for potentiometers which is simple and inexpensive to fabricate and install, which is readily capable of adjustment in position on the shaft upon which it is installed, and which can readily be adjusted as regards the phasing of the contacts over a sufiiciently large range to permit such adjustment in exact fashion to any desired value. As will be seen from the embodiment herein to be described, the present invention provides a structure in which all of the desired adjustments can be effected with a minimum of complex operations on the part of the assembler. It will be seen that in general these aims and objects are accomplished by the provision of a pair of nested collars, each carrying one of the wiper contacts, the outer collar being provided with a single fastening or clamping means having a first condition in which the collars are readily slideable with respect to each other so that they may readily be nested, a second condition in which the collars are clamped with sufficient tightness so that they hold together as an assembly, but nevertheless sufficiently loosely engaged so that relative rotation may easily be manually accomplished for the purpose of phasing the two contacts, and a third condition wherein the outer collar securely clamps the inner collar, which in turn securely clamps theshaft, so that the entire assembly is locked both rotationally and longi-v tudinally in the desired relative positions of the parts.

An additional feature of the present construction lies in the manner in which the lateral (i.e., longitudinal of the shaft) relation between the wipers is established andv as possible except for phase, it becomes important to assure that the two wipers contact the resistance element along the same line, rather than at laterally spaced points. 'This is required both from the standpoint of making uniform any variations from ideal operation due to such imperfections as may exist and also, in the case of wire-wound potentiometers, because the diiierence in resistance values obtained along the length of a single turn of the wire, although extremely small, is nevertheless of sufiicient importance to be considered in assuring that the resistance characteristics Seen by the two wipers are as identical as possible except for phase with respect to shaft rotation. The nesting of the collars in the present construction is accomplished in such a manner as to determine the longitudinal relationy between the wiper contacts so that this requires no attention on the part of the assembler. In the embodiment of the invention to be described, this constructional feature is employed to produce identity in this aspect of the relative positioning, for the reasons just stated. However, the adaptation of the principle of construction to produce other desired spacings will readily be seen. It will further be seen that the desirable features and advantages described above are achieved without substantial deviation from compactness of the contact assembly.

For more detailed understanding of the invention, and of further advantages not specifically discussed above, reference is made to the embodiment illustrated in the attached drawing, in which:

Figure l is a rear view of a .rotary potentiometer embodying the instant invention, the back cover conventionally employed being ommitted for clarity of illustration;

Figure 2 is a sectional view taken on line 2-2 of Figure l;

Figure 3 is a view in front elevation of a wiper assembly constituting a portion of the potentiometer of Figure l;

Figure 4 is a View in rear elevation of the wiper assembly; and

Figure 5 is a side view of the wiper assembly.

Referring now to the drawings, the illustrated rotary potentiometer embodying the present invention includes a conventional housing 12 which supports a wirewound resistance element 14. A pair of terminal assemblies, generally indicated by 16 and 18 respectively, are mounted on the housing 12. A pair of grooved slip rings 20 and 22 are mounted within the housing 12 as will be hereinafter described and are electrically connected to terminals of the terminal assemblies 16 and 18. A wiper assembly 24 bears wipers contacting the resistance element 14 and electrically connected to the slip rings 20 and 22.

The housing 12 includes a cylindrical metal sidewall 26 which has a front wall 28 formed integrally therewith. An insulating sheet 29 lines the inner surface of wallv 26 so that wire-wound resistance element 14 is insulated from the housing. A bearing sleeve 30 is pressfitted in an aperture in the front wall 28. A shaft 32 has a reduced portion 34 rotatably mounted in the bearing 30 and extending into the housing. The reduced portion 34 has an annular groove 36 adjacent to the bearing sleeve, in which is seated a C-washer 38 locking the shaft 32 in position longitudinally.

An annular :flanged insulating sleeve 40 is press-fitted on the bearing 30 and the slip rings 20 and 22' are mounted on the insulating sleeve 40 on insulating rings 42 and 44 respectively and the insulating rings 42 and 44 are iixed to the annular insulator by a suitable adhesive.

The manner in which the respective slip rings and resistance element taps are connected to the exterior terminals is not herein disclosed, such connections being made in the manner which is conventional in sine-cosine potentiometers.

Wiper assembly 24 is mounted on the inner end of the shaft 32. The wiper assembly has a iirst wiper unit 46 which includes a radially slotted collar 48 made of an insulating material. The central aperture 50 of the collar 48 has a diameter substantially equal to the diameter of the reduced portion 34 of shaft 32 so that there is a fairly snug fit between collar 48 and shaft 32. A flange 52 is formed integrally with collar 48. A mounting arm 54, made of a material such as beryllium bronze, is riveted to the outer surface of the flange S2 and extends back along and beyond the end of the collar 48 (for reasons that will become apparent hereinafter) substantially parallel to the axis of the collar 48. A generally U-shaped resilient contact wire 56 is attached to the mounting arm with the bottom of the U soldered to the free end of the mounting arm so that resilient arms 58 extend inwardly to engage slip ring 22. A wiper 60 is soldered to mounting arm 54 at a selected point which will be hereinafter described. The wiper 60 includes a pair of identical .resilient spring fingers 62, each of which has a bent portion 64 at its respective free end to engage the resistance element 14.

The wiper assembly also includes a second wiper unit 66 into which the above described wiper unit 46 nests. Wiper unit 66 includes a metallic split collar 68 which has an inside diameter slightly greater than the outside diameter of collar 48 so that collar 68 may be easily assembled onto collar 48. The outside diameter of collar 68 is less than the outside diameter of flange 52 of collar 48 in order to allow the two collars to move angularly relative to each other without interference from arm 54. Collar 68 has a width substantially equal to the length of collar 48 from the free end of collar 48 to ange 52 so that the ends of the two collars are substantially flush when collar 68 is nested with collar 48 and is positioned against the flange.

Split collar 68 has a tab 70 formed integral with the collar on each side of the slot or split. A machine screw 72 is threadedly mounted in one of the tabs 70 so that the collar may be drawn together to clamp collar 68 onto collar 48. The screw 72 has a head 74 which has cross slots therein to facilitate manipulation of the screw when the assembly is mounted on the shaft within the housing. i

A radially outwardly extending protrusion 76 is formed integral with the split collar 68 opposite the split in the collar. A second mounting arm 78 which has a length substantially less than the mounting arm 54 is soldered to the protrusion. Mounting arm 78, which is made of a material such as beryllium bronze, is substantially parallel to mounting arm 54 and to the common axis of the collars. A generally U-shaped resilient contact element 80 is attached to arm 78 with the bottom of the U soldered to the free end of the arm so that the resilient arms 82 extend inwardly to engage slip ring 20. A wiper 84 having a construction identical to wiper 60 is soldered to mounting arm 78 and protrusion 76.

The two wipers 60 and 84 are positioned on their respective wiper units to be in the same transverse plane when the units are assembled, 'wiper 60 being soldered to mounting arm 54 at a point below iiange 52, which point is selected to place wiper 60 in the same plane as wiper 84 when the two wiper units are nested together. Thus, the wipers engage the resistance element along the same line so that an identical resistance characteristic is obtained when one or the other wiper contacts the resistance element.

Wiper unit 66 is mounted on unit 46 by rst positioning unitv 66 between the resilient arms of contact element 56 and the end of split collar 48, the arm S4 being of sufficient length to permit the insertion of unit 66 in said position. Collar 68 is then :slipped onto the collar 48 and screw 72 is tightened enough so that there is a fairly snug fit between the two collars. Thus, the collars may be moved relative to each other but will not readily slip during assembly of the wiper assembly into the potentiometer.

The wiper assembly is placed on the end of reduced portion 34 of the shaft. 'I'he'entire assembly is pushed onto the shaft with a rotary movement so that the resilient arms slip into their respective grooved slip rings 20 and 22. Although a coarse adjustment of phasing may be made when the wiper units are assembled, the final and precise adjustment is made when the assembly is already positioned on the shaft. The final phasing adjustmentis made by inserting a tool into an aperture 86 in flange 52 to engage collar 46, and then rotating collar 68 relative to collar 46 in order to achieve proper phasing; exactness of adjustment may be monitored by electrical measuring means appropriately connected to the external terminals. It is evident that though the wiper assembly is shown with the wipers spaced approximately 90 degrees apart, the wipers may be positioned in almost any selected angular relationship. After the phasing is adjusted, the assembly is tightened on the shaft, by tightening of screw 72. In this manner wiper unit 66 is securely clamped onto wiper unit 46 and wiper unit 46 is securely clamped onto the shaft 32 at the same time and in the same operation.

It will be obvious to those skilled in the art, after careful perusal of the above description and examination of the annexed" drawings, that many changes may be made Without departing from the teachings of the invention, which may be incorporated in structures substantially different in appearance from that herein illustrated and described. Accordingly the scope of the invention shall not be deemed to be limited to the particular embodiment shown in the drawing but shall be determined by the annexed claims.

What is claimed is:

1. A Wiper contact assembly for rotary potentiometers comprising first and second wiper mounting members rotatably nested for phasing adjustment, a wiper on each wiper-mounting member, a fastener member, means responsive to operation of the fastener member for locking the wiper-mounting members -against `relative rotation in both directions and means on the axis of said relative :rotation responsive to operation of the same fastener member to lock the assembly on a potentiometer s'haft.

2. A wiper contact assembly for rotary potentiometers comprising Ia rst collar adapted to be compressed on a shaft, a second collar slidably surrounding the first collar and adapted to be compressed thereon, mutually insulated wiper members secured to the respective collars, and means for compressing the second collar on the fi-rst collar to simultaneously lock the phasing of the wipers and lock the contact assembly to a potentiometer shaft.

3. The assembly of claim 2 wherein one of said collars has a portion abutting an end of the other collar to fix the relative longitudinal position of the collars.

4. 'I 'he contact assembly of claim 3 wherein the wipers are in the same transverse plane in said position of abutment.

5. A rotary potentiometer having a housing, a resistance element mounted on said housing, a shaft rotatable in said housing, a pair of terminals on said housing, a wiper unit on the shaft electrically contacting the resistance element and electrically connected to one of said terminals, 'and a second wiper unit on the shaft electrically contacting the resistance element and electrically connected to the other of the terminals, said second wiper unit nesting over the first mentioned Wiper unit and including means for compressing the second wiper unit on the first Wiper unit, whereby the second wiper unit is clamped to the first wiper unit and the first wiper unit is clamped to the potentiometer shaft.

6. A rotary potentiometer having a housing, a resistance element mounted on said housing, a pair of contact means mounted on said housing, a terminal assembly mounted on said housing and electrically connected to each of said contact means, a shaft rotatably supported in said housing, a Iwiper unit mounted on said shaft, said wiper unit electrically connecting the resistance element with one of the contact means, and a second wiper unit nesting over the rst mentioned wiper unit, said second wiper unit electrically connecting the resi-stance element with the other of said contact means and including a fastener member and means responsive to operation of the fastener member for simultaneously securing the Wiper units to the shaft and to each other.

7. A rotary potentiometer having a housing, said housing including a cylindrical wall and a floor formed integral with said wall, a resistance element mounted on said cylindrical wall, a shaft rotatably mounted within said housing, a terminal assembly mounted on said housing, a pair of slip rings mounted within said housing and electrically connected to the terminal assembly, a split collar mounted on one end of said shaft, a mounting arm attached to said collar, a resilient contact arm fixed to said mounting arm and electrically contacting one of said slip rings, a wiper electrically contacting the resistance element and electrically connected to said mounting arm, a second split collar nestably mounted on the first mentioned split collar, a second mounting arm mounted' on the second split collar, a second resilient contact arm fixed to the second mounting arm and electrically contacting the second slip ring, a second wiper electrically contacting the resistance element and electrically connected to the second mounting arm, and means for clamping the second split collar to the first split collar-and simultaneously clamping the first split collar to the shaft.

8. A wiper assembly for use in a rotary potentiometer, said assembly comprising a collar adapted for mounting on a potentiometer shaft, a wiper mounted on said collar, a contact arm mounted on said collar and electrically connected to said wiper, a second collar mounted on the first mentioned collar, a second wiper mounted on the second collar, a second arm attached to the second collar and electrically connected to the wiper, and means associated with said second collar for clamping the second collar to the first mentioned collar and simultaneously securing the first mentioned collar to a potentiometer shaft.

9. A wiper assembly for use in a rotary potentiometer, said assembly comprising a resilient split collar having a tab outwardly extending from each end of the collar, an adjusting screw threadedly mounted in one of said tabs, a wiper mounted on said collar, a second spit collar nesting with the first mentioned collar, a mounting arm secured to the second mentioned collar, and a second wiper secured to the mounting Iarm in the same plane as the first mentioned wiper, whereby the two wipers may be positioned with a selected angle therebetween and the adjustment screw is selectively tightened -to hold the two collars, thereby locking the wipers in selected relative positions.

10. A rotary potentiometer having a housing, a resistance element mounted in said housing, a potentiometer shaft rotatably mounted in said housing, a wiper electrically contacting said resistance element, a contact arm electrically connected-to the wiper, a contact ring mounted on said housing and electrically contacting said contact arm, a terminal assembly mounted on said housing and electrically connected to the contact ring, a second wiper electrically contacting the resistance element, a second arm electrically connected to the second wiper, a second contact Iring mounted on -the housing electrically connected to the terminal assembly and electrically contacting the second contact arm, a split collar supporting the first mentioned wiper and contact arm, a second split collar nesting with the first mentioned spit collar supporting the second mentioned wiper and contact arm, the second spit collar mounted on the potentiometer shaft, a pair of ltabs fixed to the first mentioned spit collar on opposite sides of the split, and a screw threadedly mounted in one of said tabs, whereby the screw is tightened to clamp the rst mentioned collar on to the second mentioned collar `and simultaneously clamp the second mentioned collar to .the potentiometer shaft.

11. A Wiperassembly for use in 1a rotary potentiometer comprising a spit resilient collar, a wiper mounted on said collar, a contact arm mounted on said collar and electrically connected to the wiper, a second spit collar nesting within the rst split collar, a mounting arm xed to the second split collar, a Wiper mounted on said mounting arm in the same-plane as the first mentioned wiper, a Contact arm iiXed to the mounting arm, and means associated with the rst mentioned collar for clamping the first mentioned collar to the second mentioned collar and reducing the inside diameter of the second mentioned collar, whereby a selected relative angular position between the twowipers may be xed by the aforementioned means 12. A wiper assembly for use in a rotary potentiometer comprising a first Wiper unit including a resilient split collar, a wiper mounted on said collar, means associated with said collar for decreasing the inside diameter of said collar, and a contact element :attached to said collar, said contact element having an -arm spaced from said collar and adapted to electrically contacta slip ring, and a second wiper unit nesting with the first Wiper unit, said second Wiper unit including a resilient insulating split collar mounted within the rst mentioned split collar, said insulating split collar having its central xaperture adapted to receive a shaft, a mounting arm secured to the insulating split collar substantially parallel tothe axis of the aperture in said collar, said arm extending beyond the end of said second collar a suicient distance to receivc the irst mentioned wiper unit between the end of the arm and the end of fthe second mentioned collar, a second wiper secured to the mounting arm in the same plane as the rst mentioned wiper in the rst wiper unit, and a second contact element mounted on the end of said mounting arm. t

13. In a potentiometer, a wiper drive member, a first wiper-mounting member adjustably positioned on the drive member, a second wiper-mounting member adjustably poistioned on the first mounting member, a single manually operable locking member, and means responsive to operation of the single locking member to lock the first mounting member in position on the drive member and the second mounting member in position on the rst.

14. In a potentiometer, a wiper drive member, a rst wiper-mounting member having a portion slideably positioned on the drive member, a second wiper-mounting member having a portion slideably positioned on the first mounting member, a clamping member, and means re. sponsive to operation of the clamping member to compress said portions of the mounting members to lock the entire assembly.

References Cited in the le of this patent UNITED STATES PATENTS Rich Mar. 3l, 1942 2,881,295 Brown Apr. 7, 1959 

